When a well, such as an oil or gas well, is at the end of its useful life it is usually abandoned. In other situations (e.g. due to low oil prices, “workovers” and other events such as approaching storms or hurricanes) a well may need to be temporarily suspended. However before a well can be abandoned/suspended the well must be “plugged” to ensure that potentially hazardous materials, such as hydrocarbons, cannot escape the well.
In the past various methods have been employed to plug abandoned wells. One such known method involves pouring cement or resin into a well so as to fill a length of the well. However the use of cement/resin has proven to be unreliable and vulnerable to leaking. This can lead to previously abandoned wells being re-plugged at considerable extra expense.
In view of the limitations of using cement/resin to plug wells an alternative approach was developed which uses a bismuth-containing alloy to form a seal within the well. This approach, which is described in detail in CA 2592556 and U.S. Pat. No. 6,923,263, makes use of the fact that such alloys contract upon melting and expand again when they re-solidify. Essentially the alloy is deployed into a well; heated until it melts and “slumps”; and then allowed to cool whereby the alloy expands to form a tight seal with the walls of the well.
The use of eutectic alloys, such as bismuth-containing alloys, to plug wells or repair existing plugs in wells is described in: U.S. Pat. No. 7,290,609; U.S. Pat. No. 7,152,657; US 2006/0144591; U.S. Pat. No. 6,828,531; U.S. Pat. No. 6,664,522; U.S. Pat. No. 6,474,414; and US 2005/0109511.
International PCT application WO2011/151271 describes a number of improvements relating to methods and apparatus for use in well abandonment.